* guix/scripts/substitute-binary.scm (%narinfo-cache-directory,
%narinfo-ttl, %narinfo-negative-ttl): New variables.
(with-atomic-file-output, object->fields, read-narinfo,
write-narinfo, narinfo->string, string->narinfo, lookup-narinfo): New
procedures.
(fetch-narinfo): Adjust to use `read-narinfo'.
(guix-substitute-binary): Ensure the existence of
%NARINFO-CACHE-DIRECTORY. Use `lookup-narinfo' instead of
`fetch-narinfo'.
This allows build outputs to be transparently downloaded from
http://hydra.gnu.org, for example.
* config-daemon.ac: Check for `gzip', `bzip2', and `xz'.
* guix/config.scm.in (%gzip, %bzip2, %xz): New variable.
* guix/scripts/substitute-binary.scm (fetch): Return SIZE as a second value.
(<narinfo>): Change `url' to `uri'.
(make-narinfo): Rename to...
(narinfo-maker): ... this. Handle relative URLs.
(fetch-narinfo): Adjust accordingly.
(filtered-port, decompressed-port): New procedures.
(guix-substitute-binary): Implement the `--substitute' case.
* tests/store.scm ("substitute query"): Use (%store-prefix) instead
of (getenv "NIX_STORE_DIR").
("substitute"): New test.
* guix/scripts/substitute-binary.scm: New file.
* Makefile.am (MODULES): Add it.
* nix/scripts/substitute-binary.in: New file.
* config-daemon.ac: Produce nix/scripts/substitute-binary.
* daemon.am (nodist_pkglibexec_SCRIPTS): Add
nix/scripts/substitute-binary.
* guix/store.scm (substitutable-path-info): Use the
`query-substitutable-path-infos' RPC.
* nix/nix-daemon/guix-daemon.cc (main): Honor `NIX_SUBSTITUTERS'.
* pre-inst-env.in: Set `NIX_SUBSTITUTERS'.
* test-env.in: Leave `NIX_SUBSTITUTERS' unchanged. Set
`GUIX_BINARY_SUBSTITUTE_URL, and create
$NIX_STATE_DIR/substituter-data.
Run `guix-daemon' within `./pre-inst-env'.
* tests/store.scm ("substitute query"): New test.
* guix/store.scm (gc-action): New enumerate type.
(read-long-long, read-string-list, write-store-path,
write-store-path-list, read-store-path-list): New procedures.
(write-arg): Add support for `store-path' and `store-path-list'.
(read-arg): Add support for `store-path-list'.
(define-operation): Add support for multiple-value returns.
(run-gc, live-paths, dead-paths, collect-garbage, delete-paths): New
procedures.
(%long-long-max): New macro.
* tests/store.scm: New file.
* Makefile.am (TESTS): Add it.
